Assign (some) minimum frame size to the Overpass API download entry field

[Skybunny]

What steps will reproduce the problem?

1. Do an Overpass API query. Possibly resize the download box.
2. Open it again to do another query, possibly after restarting JOSM.
3. See screenshot.

What is the expected result?

The box should be the default size one expects when starting JOSM for the first time or otherwise.

What happens instead?

(Screenshot)

Please provide any additional information below. Attach a screenshot if possible.

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2018-07-21 00:36:46 +0200 (Sat, 21 Jul 2018)
Revision:14040
Build-Date:2018-07-21 01:32:00
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (14040 en) Mac OS X 10.14
OS Build number: Mac OS X 10.14 (18A336e)
Memory Usage: 267 MB / 5120 MB (98 MB allocated, but free)
Java version: 10.0.1+10, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Screen: Display 69680128 1440x900
Maximum Screen Size: 1440x900

Plugins:
+ pbf (34389)

Last errors/warnings:
- W: Update plugins - org.openstreetmap.josm.plugins.PluginHandler$UpdatePluginsMessagePanel[,0,0,0x0,invalid,layout=java.awt.GridBagLayout,alignmentX=0.0,alignmentY=0.0,border=,flags=9,maximumSize=,minimumSize=,preferredSize=]
- W: No configuration settings found.  Using hardcoded default values for all pools.